memory card loses space over time?

"Arte Phacting" wrote in message ...
This sounds reasonable - as far as the original poser is concerned does
he/she have a claim to having a faulty card as the error correction is
kicking in at too high a rate?
....
I hear that the more you use a photo card, the less it holds, why
is this?
....
Most Compact Flash cards (and probably memory sticks, secure digital,
and the rest) have built-in error detection and remapping. If a spot
on the card dies from age or use, it is detected and mapped out of
the writeable area on the card. That way you don't end up writing
part of an image onto a non-retrievable portion of the card. As a
card ages and develops more dead spots, the amount of storage
available drops.
....

(This is based on my experience with CF cards and investigations into wear leveling for
a high usage application...)

While this might sound reasonable, it is not the way flash memory is designed. Unlike hard
drives (where the entire area is used at the beginning), flash memories have a "spares" pool
in excess of the stated size. As areas of memory fail, the failed areas are mapped to
members of the spares pool. The device does not "fail" or loose capacity until the spares
pool is exhausted. Even for commercial (versus military) devices, this shouldn't happen
in normal user life times.

(The application I was investigating wrote the entire card every 6 minutes or so, continuously
for days. We were able to "wear out" the flash memory, but it took days.)

The two most likely explanations a
1. The original claim is an urban legend. (My belief from my own experiences both with
cameras and commercial applications.)
2. The camera or computer is leaving old files on the device. A format of the card (preferably
in the camera to avoid format mistakes by the user) should always return the device
to its original capacity.
3. An actual case of early failure of a device has erroneously been extrapolated as usual
device behavior.


--
Dan (Woj...) dmaster at lucent dot com
----------------------------------
"What can you see / On the horizon?
Why do the white gulls call?
Across the sea / A pale moon rises.
The ships have come / To carry you home.
And all will turn to silver glass.
A light on the water / All souls pass."

In message , Dan Wojciechowski
writes
"Arte Phacting" wrote in message
...
This sounds reasonable - as far as the original poser is concerned does
he/she have a claim to having a faulty card as the error correction is
kicking in at too high a rate?
...
I hear that the more you use a photo card, the less it holds, why
is this?
...
Most Compact Flash cards (and probably memory sticks, secure digital,
and the rest) have built-in error detection and remapping. If a spot
on the card dies from age or use, it is detected and mapped out of
the writeable area on the card. That way you don't end up writing
part of an image onto a non-retrievable portion of the card. As a
card ages and develops more dead spots, the amount of storage
available drops.
...

(This is based on my experience with CF cards and investigations into
wear leveling for
a high usage application...)

While this might sound reasonable, it is not the way flash memory is
designed. Unlike hard
drives (where the entire area is used at the beginning), flash memories
have a "spares" pool
in excess of the stated size. As areas of memory fail, the failed
areas are mapped to
members of the spares pool. The device does not "fail" or loose
capacity until the spares
pool is exhausted. Even for commercial (versus military) devices, this
shouldn't happen
in normal user life times.

(The application I was investigating wrote the entire card every 6
minutes or so, continuously
for days. We were able to "wear out" the flash memory, but it took days.)

The two most likely explanations a
1. The original claim is an urban legend. (My belief from my own
experiences both with
cameras and commercial applications.)
2. The camera or computer is leaving old files on the device. A format
of the card (preferably
in the camera to avoid format mistakes by the user) should always
return the device
to its original capacity.
3. An actual case of early failure of a device has erroneously been
extrapolated as usual
device behavior.

All the ones I have ever seen that have "lost" capacity had been mounted
and/or browsed by "clever" applications that leave large thumbnail index
files. eg. PSPro *.jbf, XP *.db These can gradually accumulate in
subdirectories.

As you said, a reformat in the camera should restore full capacity
again.

Regards,
--
Martin Brown

I wonder if we are in the process of replacing one urban myth with another?

Is there not a hard & fast test method - an ISO standard on memory chips?

Arty

ps - Dan, way to go mate

A

"Martin Brown" wrote in message
...
In message , Dan Wojciechowski
writes
"Arte Phacting" wrote in message
...
This sounds reasonable - as far as the original poser is concerned does
he/she have a claim to having a faulty card as the error correction is
kicking in at too high a rate?
...
I hear that the more you use a photo card, the less it holds, why
is this?
...
Most Compact Flash cards (and probably memory sticks, secure digital,
and the rest) have built-in error detection and remapping. If a spot
on the card dies from age or use, it is detected and mapped out of
the writeable area on the card. That way you don't end up writing
part of an image onto a non-retrievable portion of the card. As a
card ages and develops more dead spots, the amount of storage
available drops.
...

(This is based on my experience with CF cards and investigations into
wear leveling for
a high usage application...)

While this might sound reasonable, it is not the way flash memory is
designed. Unlike hard
drives (where the entire area is used at the beginning), flash memories
have a "spares" pool
in excess of the stated size. As areas of memory fail, the failed
areas are mapped to
members of the spares pool. The device does not "fail" or loose
capacity until the spares
pool is exhausted. Even for commercial (versus military) devices, this
shouldn't happen
in normal user life times.

(The application I was investigating wrote the entire card every 6
minutes or so, continuously
for days. We were able to "wear out" the flash memory, but it took
days.)

The two most likely explanations a
1. The original claim is an urban legend. (My belief from my own
experiences both with
cameras and commercial applications.)
2. The camera or computer is leaving old files on the device. A format
of the card (preferably
in the camera to avoid format mistakes by the user) should always
return the device
to its original capacity.
3. An actual case of early failure of a device has erroneously been
extrapolated as usual
device behavior.

All the ones I have ever seen that have "lost" capacity had been mounted
and/or browsed by "clever" applications that leave large thumbnail index
files. eg. PSPro *.jbf, XP *.db These can gradually accumulate in
subdirectories.

As you said, a reformat in the camera should restore full capacity
again.

Regards,
--
Martin Brown